This application relates to improvements in electrical commutators for use on two relatively rotating parts.
In the prior art, rotating electrical commutators are utilized to transfer electrical communication between two parts that rotate relative to each other. In one common application, electrical communication between a steering wheel and the fixed steering column is provided by any one of several types of commutators. Since the steering wheel must rotate through several rotations relative to the fixed steering column, some method of communicating electrical signals between the steering wheel and the fixed steering column is necessary that can accommodate relative rotation.
In one standard steering wheel electrical commutator, a wire ribbon physically connects a rotating member to a connection on a fixed member. The wire ribbon is coiled such that several complete relative rotations are allowed. Prior art wire ribbons accommodate approximately three and one-half complete rotations of the steering wheel relative to the fixed steering column in either direction. While this may be adequate rotation, there are some deficiencies in the wire ribbon type of connection.
First, wire ribbons do not allow the use of more than one connection at any axial space. Thus, as the number of electrical communications that must be transferred from the steering wheel to the fixed steering column increase, the required axial length for a commutator utilizing wire ribbons also increases dramatically. Modem vehicle steering systems must communicate many distinct electrical signals between the steering wheel and the fixed steering column. As an example, steering wheels now must carry signals from the cruise control, the air bag system, and the horn. Moreover, other controls such as those for the radio or lights are being designed into the steering wheel. Thus, electrical commutators are needed that will reliably communicate many electrical signals between the rotating steering wheel and the fixed steering column. The relatively large wire ribbons would require excessive amounts of axial space to communicate all of the required signals.
In any automotive environment, it is necessary to minimize the required space. Thus, due to the large axial space requirements, wire ribbon commutators have limited application.
In addition, while wire ribbons are capable of providing acceptable amounts of relative rotation, they may only do so when they have been precisely mounted between the rotating and fixed members. That is, the wire ribbon may be able to provide three and one-half complete rotations in either the clockwise or counterclockwise direction, but only when the wire ribbon has been properly mounted between the rotating and non-rotating members. Should the wire ribbon be mounted improperly, it could, as an example, allow six complete rotations in a first direction, but only one in the other direction. This would, of course, be undesirable.
The other main type of steering wheel commutator has been a single connection point that rotates with the rotating member along a ring on the fixed member. Such commutators do not require the precise positioning of wire ribbons, nor do they require large amounts of axial space. However, the single contact point rotary commutators have not always operated as desired. As one example, should the single contact point break or bend out of contact with the ring, there is no longer any electrical communication between the rotating and fixed member.
With the prior art single contact points, contamination or dirt on either the contact point or the ring could cause the contact point to come out of electrical communication with the ring. In addition, with a single contact point, should there be a scratch or bump at any radial location on the ring, the electrical contact could move out of contact with the ring, thus breaking the electrical circuit. Also, the vibration on the connection could cause the single electrical contact to come out of contact with the ring. This is, of course, undesirable.
There has been one proposed system that utilized several wires held in contact with a ramped ring. This system would not be capable of transmitting several signals and also requires undue axial space.
Similarly, the prior art single contact points extend at an angle toward the other ring. The angle orientation in the clockwise direction could cause more resistance to turning in the counter-clockwise direction and vice versa. Moreover, the integrity of the electrical connection would also be different between the clockwise and counter-clockwise directions.